A hybrid vehicle may include a driveline disconnect clutch for selectively mechanically coupling an engine to a motor and transmission. The disconnect clutch may allow the motor to propel the vehicle while the engine is stopped to reduce an amount of energy used to propel the hybrid vehicle. The motor may operate more efficiently than the engine where the vehicle is being operated at low speeds and low driver demand torque levels. Therefore, it may be desirable to not operate the engine at low vehicle speeds and low driver demand torque levels to conserve hydrocarbon based fuel. Nevertheless, if a driver increases a driver demand torque, the driveline disconnect clutch may be closed to increase torque output from the vehicle's driveline to meet driver demand torque. To reduce a possibility of driveline degradation, a driveline disconnect clutch having a large inertia may be needed to allow the driveline disconnect clutch to operate over a wide range of driveline operating conditions. However, if a driveline disconnect clutch has a large inertia and is installed in the hybrid vehicle, vehicle fuel economy may degrade. Therefore, it may be desirable to provide a hybrid vehicle that includes a lower inertia driveline disconnect clutch, but exhibits a reduced possibility of driveline degradation.
The inventors herein have recognized the above-mentioned disadvantages and have developed a driveline method, comprising: closing an open driveline disconnect clutch in response to an estimated motor speed after a requested transmission gear downshift.
By estimating a speed of a motor in response to a requested transmission gear downshift, it may be possible to provide the technical result of reducing driveline disconnect degradation. Specifically, a speed that a motor rotates immediately after a new gear is engaged may be a basis for judging whether or not to close a driveline disconnect clutch before the new gear is actually engaged. If the motor speed after engaging the new gear would be greater than a threshold speed, an open driveline disconnect clutch may be closed before the new gear is engaged to reduce the possibility of driveline disconnect clutch degradation. For example, if a driver manually requests a lower gear than a present gear, an open driveline disconnect clutch may be closed if engaging the lower gear would increase motor speed to a speed where increased driveline disconnect clutch degradation may be present when the driveline disconnect clutch is closed. The lower gear may be engaged after the driveline disconnect clutch is closed. In this way, it may be possible to avoid operating the driveline disconnect clutch at speeds where driveline disconnect clutch closing may cause driveline disconnect clutch degradation. Consequently, it may be possible to operate the driveline with a driveline disconnect clutch that has lower inertia.
The present description may provide several advantages. For example, the approach may reduce the possibility of driveline disconnect clutch degradation. Further, the approach may increase vehicle efficiency by lowering driveline inertia while still allowing the driveline to operate over a wide range of operating conditions. Additionally, the approach may provide a way to anticipate and prepare for the possibility of higher driver demand torque.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.